Preparation method and application of electrochemically prepared boron-nitrogen-doped carbon nanofiber-based water electrolysis catalytic material

Abstract

A preparation method and application of an electrochemically prepared water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers. First, lithium perchlorate, pyrrole, sodium carbonate / sodium bicarbonate buffer and deionized water are evenly mixed, and then an electrochemical reaction is carried out at a constant potential to grow nanofibers on a nickel foam electrode. The nanofibers are immersed in a boric acid solution, and then the boron-doped nanofibers are carbonized at high temperature to obtain boron-nitrogen-doped carbon nanofibers. Nickel sulfate and ferrous sulfate solutions are prepared, and then an electrochemical reaction is carried out to obtain a fiber core-shell catalyst. The fiber core-shell catalyst of the present invention has a core layer of boron-nitrogen-doped carbon nanofibers, which have the advantages of high electrochemical active area, high stability, high physical strength, low electrochemical impedance and super hydrophilicity, and a shell layer of nickel-iron layered double hydroxide, which has the characteristics of high catalytic activity. The coupling of the shell layer and the core layer not only gives the catalyst the above advantages, but also greatly enhances the intrinsic catalytic activity and stability of the shell nickel-iron.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and specifically relates to a method for preparing a bifunctional catalyst for water electrolysis, and more particularly to a method for preparing and applying a boron-nitrogen-doped carbon nanofiber catalytic material. Background Art

[0002] The extensive use of fossil energy has affected the global carbon balance and exacerbated the greenhouse effect. Using clean energy to replace fossil energy has become an inevitable choice for the sustainable development of human society. Among all renewable energy sources, hydrogen energy has become the best choice to replace traditional fossil energy due to its clean and efficient characteristics. The use of renewable energy to produce hydrogen through water electrolysis is considered to be the forefront and research hotspot of hydrogen energy technology. The development of bifunctional catalytic materials for the complete decomposition of water that can be used for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), and improving their activity and stability on the electrode are the keys to efficient water electrolysis for hydrogen production.

[0003] Electrolytic water catalytic materials require a substrate with a high specific surface area. Polymer-based fibrous materials can be used as the substrate of electrolytic water composite materials due to their unique structure and properties. Regarding the preparation methods of such materials, previous technologies have focused on using chemical synthesis to prepare polymers (CN104289249A, CN107768622B, CN107768622B, CN105024050B, CN106298269B, CN106098404B, CN103700818A) or using electrospinning to prepare polymer fibers (CN104342852B, CN106450181B, CN110616561B) and nitrogen-doped carbon nanocomposites (CN109248703B). It should be noted that the mainstream preparation technologies all study powder catalysts, which require the addition of adhesives to adhere to the electrodes. On the one hand, because the electrolysis of water is accompanied by a strong gasification effect at high current density, the bound powdered material easily falls off the electrode surface during the reaction, which is not conducive to the durability of the catalytic material. On the other hand, the addition of binders inevitably causes the powdered catalyst to suffer a decrease in conductivity and covers its active sites, resulting in a decrease in the electrolysis activity of the catalytic material. Therefore, it is necessary to adopt new methods to prepare electrocatalysts with high catalytic activity, high structural stability and high conductivity for application in water electrolysis at high current density.

[0004] The current research hotspot of the technology is to further load metals and their compounds on the substrate to form a composite catalytic material. These works have made useful attempts on composite water electrolysis materials: Patent CN110052282B prepared a transition metal phosphide / core-shell nitrogen-doped carbon nanofiber composite material, Patent CN109012704A disclosed a nano-cobalt diselenide-loaded carbon nanofiber composite material, and CN113969413A disclosed a porous carbon nanofiber electrocatalyst loaded with cobalt phosphide. Looking at the existing technology, due to the limitations of the preparation method of carbon nanofibers themselves and the lack of sufficient modification treatment, the hydrophilicity of the carbon fibers themselves is poor, the electrolyte cannot completely infiltrate the substrate, and the catalyst's actual available electrochemical surface area is small, which has a serious impact on the subsequent electrodeposition step and cannot obtain a sufficiently uniform coating and sufficiently high activity water electrolysis material. In addition, the limitations of the doping elements also make it impossible for the substrate itself to effectively modulate the electronic structure of the composite catalytic material, so that the catalytic activity of the material needs to be further improved.

[0005] Therefore, the present invention discloses a preparation method and application of an electrochemically prepared water electrolysis catalytic material based on boron nitrogen-doped carbon nanofibers (BN-CNF). This material uses an electrochemical method to in-situ grow carbon nanofibers on the surface of a substrate, effectively improving the stability of the catalytic material. The fiber substrate material has a unique nanoscale three-dimensional network, providing a sufficiently large surface area. On the one hand, the doping of the substrate material with boron and nitrogen modulates the hydrophilicity of the material, ensuring the uniform electroplating of the subsequent compound active phase coating, and enhancing the water electrolysis catalytic activity by increasing the electrochemical active area; on the other hand, the boron and nitrogen doping modulates the electronic structure of the carbon fiber substrate, effectively improving the intrinsic activity of the composite water electrolysis catalytic material. Summary of the Invention

[0006] The purpose of the present invention is to provide a new method for preparing a water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers.

[0007] The technical solution of the present invention:

[0008] A method for preparing an electrochemically prepared water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers, comprising the following steps:

[0009] The water electrolysis catalytic material described above is a fiber core-shell structure catalyst composed of nickel-iron compound wrapped with boron-nitrogen-doped carbon nanofibers (abbreviated as BN-CNF@NiFe, if the electrode carrier is nickel foam, it is marked as / NF). Its synthesis method has the following characteristics:

[0010] a. Lithium perchlorate, pyrrole, sodium carbonate / sodium bicarbonate buffer, and deionized water were mixed and stirred to form a uniform mixture. Then, nickel foam was used as the working electrode and polymerization was carried out at a constant potential of 0.85 V under a three-electrode system for 800 seconds. The polymer was then impregnated with a boric acid solution to obtain an electrode on which boron-doped polymer nanofibers were grown.

[0011] b The electrode obtained in step a was placed in an inert gas atmosphere in a tube furnace and calcined to obtain a boron and nitrogen-doped carbon nanofiber electrode;

[0012] c. Nickel sulfate, ferrous sulfate, and deionized water were mixed and stirred to form a uniform mixture. Then, a boron-nitrogen-doped carbon nanofiber electrode was used as the working electrode and electrodeposition was performed at a constant potential of -5 V for 120 seconds in a three-electrode system to obtain a water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers.

[0013] The boric acid solution is one of boric acid aqueous solution, boric acid methanol solution, and boric acid ethanol solution, or a mixture of two or more thereof.

[0014] The immersion time of the boric acid solution is 1 to 48 hours.

[0015] The concentration of the boric acid solution is 1 g / mL to a saturated solution.

[0016] The inert gas is one of helium, argon, and nitrogen, or a mixture of two or more.

[0017] The calcination temperature is 400° C. to 1000° C., and the calcination time is 30 min to 200 min.

[0018] The molar ratio of the nitrogen-containing organic monomer to other raw materials is: n(pyrrole) / n(lithium perchlorate)=0.1-10, n(pyrrole) / n(sodium carbonate)=0.1-10, n(pyrrole) / n(sodium bicarbonate)=0.1-10, and n(H2O) / n(pyrrole)=100-2000.

[0019] The molar ratio of the nickel source to other raw materials is: n(Ni) / n(Fe)=5-10, n(H2O) / n(Ni)=100-2000.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The core of the electrocatalyst is a three-dimensional network nanostructure woven from boron and nitrogen-doped carbon nanofibers, which has a very high electrochemically active surface area and provides abundant pore channels to help the gas generated by water electrolysis escape.

[0022] (2) The incorporation of boron reduces the impedance of carbon materials and increases the electron transfer rate.

[0023] (3) The shell and core of NiFe layered double hydroxide have a synergistic effect, resulting in more active sites and higher activity. The rearrangement of charge density between the core and shell caused by boron and nitrogen doping and the accumulation of holes on the Ni site lead to more Ni 3+ The generation of Ni 3+ It is the key active site for oxygen evolution reaction.

[0024] (4) (BN-CNF@NiFe) / NF has significant advantages in the electrocatalytic water splitting reaction: (BN-CNF@NiFe) / NF has a high electrocatalytic activity at a current density of 100 mA cm -2 The overpotentials of OER and HER were 238 mV and 126 mV, respectively. When (BN-CNF@NiFe) / NF electrode was used as both anode and cathode for water electrolysis, the voltage was 1.75 V@100 mA cm -2 , and has good stability; under commercial hydrogen production conditions of 80℃+6M KOH, (BN-CNF@NiFe) / NF simultaneously exhibits high activity and high stability, and the electrolytic cell voltage of electrocatalytic full water splitting is 1.48V@100mA cm -2 , 1.69V@500mA cm -2 and 1.92V@1000mA cm -2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Electrochemical impedance spectroscopy of (BN-CNF@NiFe) / NF prepared in Example 1 of the present invention and NiFe / NF prepared in Comparative Example 1 under the test conditions of 20°C + 1M KOH.

[0026] Figure 2 Polarization curves of the electrocatalytic hydrogen evolution reaction of (BN-CNF@NiFe) / NF prepared in Example 1 of the present invention and NiFe / NF prepared in Comparative Example 1 under the test conditions of 20°C + 1M KOH.

[0027] Figure 3 Polarization curves of the electrocatalytic oxygen evolution reaction of (BN-CNF@NiFe) / NF prepared in Example 1 of the present invention and NiFe / NF prepared in Comparative Example 1 under the test conditions of 20°C + 1M KOH.

[0028] Figure 4 This is a scanning electron microscope image of (BN-CNF@NiFe) / NF prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0030] Example 1

[0031] A method for preparing an electrochemically prepared water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers comprises the following steps:

[0032] (1) First, 0.1 mol of sodium carbonate and 0.1 mol of sodium bicarbonate were dissolved in 150 mL of deionized water to prepare a buffer solution. Then, 0.01 mol of lithium perchlorate and 0.07 mol of pyrrole were added and stirred to form a uniform aqueous solution.

[0033] (2) using the aqueous solution obtained in step (1) as a three-electrode electrolytic cell, with nickel foam as the working electrode, platinum sheet as the counter electrode, and calomel electrode as the reference electrode, polymerizing at a potential of 0.85 V for 800 seconds, and washing and drying to obtain polymer nanofibers;

[0034] (3) immersing the polymer nanofibers obtained in step (2) in a saturated ethanol solution of boric acid for 12 hours to obtain boron-doped nanofibers;

[0035] (4) placing the boron-doped nanofibers obtained in step (3) in a tube furnace and calcining them at 700° C. for 120 minutes in an argon atmosphere to obtain boron-nitrogen-doped nanofibers, which are referred to as BN-CNF / NF;

[0036] (5) Dissolve 0.09 mol nickel sulfate and 0.01 mol ferrous sulfate in 100 mL of deionized water to prepare an electrolyte;

[0037] (6) The solution obtained in step (5) was used as an electrolyte, the BN-CNF / NF obtained in step (4) was used as a working electrode, a platinum sheet was used as a counter electrode, and a Hg / HgO electrode was used as a reference electrode. Electrodeposition was performed at a potential of -5 V for 120 seconds. After washing and drying the electrodes, a boron-nitrogen-doped carbon nanofiber-based water electrolysis catalytic material was obtained, which was recorded as (BN-CNF@NiFe) / NF.

[0038] Figure 1 Electrochemical impedance spectroscopy (EIS) of (BN-CNF@NiFe) / NF prepared in Example 1 and NiFe / NF prepared in Comparative Example 1 at 20°C in 1M KOH. As shown, the charge transfer resistance of (BN-CNF@NiFe) / NF is only 0.925Ω, and the internal resistance is only 0.961Ω. Both the charge transfer resistance and internal resistance of (BN-CNF@NiFe) / NF are lower than those of the comparative example.

[0039] Figure 2Polarization curves of the electrocatalytic hydrogen evolution reaction of (BN-CNF@NiFe) / NF prepared in Example 1 of the present invention and NiFe / NF prepared in Comparative Example 1 under 20°C + 1M KOH test conditions. As can be seen from the figure, (BN-CNF@NiFe) / NF achieved 100mAcm -2 At a current density of only 126 mV, the HER overpotential of (BN-CNF@NiFe) / NF is superior to that of the comparative example.

[0040] Figure 3 Polarization curves of the electrocatalytic hydrogen evolution reaction of (BN-CNF@NiFe) / NF prepared in Example 1 of the present invention and NiFe / NF prepared in Comparative Example 1 under the test conditions of 20°C + 1M KOH. Polarization curves of the electrocatalytic oxygen evolution reaction. As can be seen from the figure, (BN-CNF@NiFe) / NF achieved 100mA cm -2 Only 238 mV of OER overpotential is required at a current density of 100 mV, and the OER catalytic performance of (BN-CNF@NiFe) / NF is better than that of the comparative example.

[0041] Figure 4 This is a scanning electron microscope image of the (BN-CNF@NiFe) / NF prepared in Example 1 of the present invention. As can be seen, the catalyst has a porous, interwoven three-dimensional network structure. This morphology provides abundant reaction sites, which not only facilitates electron transport and ion adsorption but also provides channels for electrolyte penetration and bubble escape, enhancing the activity of the water splitting reaction on the catalyst surface.

[0042] Example 2

[0043] A method for preparing an electrochemically prepared water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers comprises the following steps:

[0044] (1) First, 0.3 mol of sodium carbonate and 0.2 mol of sodium bicarbonate were dissolved in 150 mL of deionized water to prepare a buffer solution. Then, 0.02 mol of lithium perchlorate and 0.1 mol of pyrrole were added and stirred to form a uniform aqueous solution.

[0045] (2) using the aqueous solution obtained in step (1) as a three-electrode electrolytic cell, with nickel foam as the working electrode, platinum sheet as the counter electrode, and calomel electrode as the reference electrode, polymerizing at a potential of 0.85 V for 800 seconds, and washing and drying to obtain polymer nanofibers;

[0046] (3) immersing the polymer nanofibers obtained in step (2) in a 2 g / mL boric acid methanol solution for 30 hours to obtain boron-doped nanofibers;

[0047] (4) placing the boron-doped nanofibers obtained in step (3) in a tube furnace and calcining them at 600° C. for 100 minutes in an argon atmosphere to obtain boron-nitrogen-doped nanofibers, which are referred to as BN-CNF / NF;

[0048] (5) Dissolve 0.05 mol nickel sulfate and 0.01 mol ferrous sulfate in 100 mL of deionized water to prepare an electrolyte;

[0049] (6) The solution obtained in step (5) was used as an electrolyte, the BN-CNF / NF obtained in step (4) was used as a working electrode, a platinum sheet was used as a counter electrode, and a Hg / HgO electrode was used as a reference electrode. Electrodeposition was performed at a potential of -5 V for 120 seconds. After washing and drying the electrodes, a boron-nitrogen-doped carbon nanofiber-based water electrolysis catalytic material was obtained, which was recorded as (BN-CNF@NiFe) / NF.

[0050] Example 3

[0051] A method for preparing an electrochemically prepared water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers comprises the following steps:

[0052] (1) First, 0.1 mol of sodium carbonate and 0.9 mol of sodium bicarbonate were dissolved in 150 mL of deionized water to prepare a buffer solution. Then, 0.04 mol of lithium perchlorate and 0.07 mol of pyrrole were added and stirred to form a uniform aqueous solution.

[0053] (2) using the aqueous solution obtained in step (1) as a three-electrode electrolytic cell, with nickel foam as the working electrode, platinum sheet as the counter electrode, and calomel electrode as the reference electrode, polymerizing at a potential of 0.85 V for 800 seconds, and washing and drying to obtain polymer nanofibers;

[0054] (3) immersing the polymer nanofibers obtained in step (2) in a saturated aqueous solution of boric acid for 12 hours to obtain boron-doped nanofibers;

[0055] (4) The boron-doped nanofibers obtained in step (3) were placed in a tube furnace and calcined at 700° C. for 150 minutes in an argon atmosphere to obtain boron-nitrogen-doped nanofibers, which were designated as BN-CNF / NF.

[0056] (5) Dissolve 0.1 mol nickel sulfate and 0.02 mol ferrous sulfate in 100 mL of deionized water to prepare an electrolyte;

[0057] (6) The solution obtained in step (5) was used as an electrolyte, the BN-CNF / NF obtained in step (4) was used as a working electrode, a platinum sheet was used as a counter electrode, and a Hg / HgO electrode was used as a reference electrode. Electrodeposition was performed at a potential of -5 V for 120 seconds. After washing and drying the electrodes, a boron-nitrogen-doped carbon nanofiber-based water electrolysis catalytic material was obtained, which was recorded as (BN-CNF@NiFe) / NF.

[0058] Example 4

[0059] A method for preparing an electrochemically prepared water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers comprises the following steps:

[0060] (1) First, 0.2 mol of sodium carbonate and 0.09 mol of sodium bicarbonate were dissolved in 150 mL of deionized water to prepare a buffer solution. Then, 0.02 mol of lithium perchlorate and 0.08 mol of pyrrole were added and stirred to form a uniform aqueous solution.

[0061] ((2) The aqueous solution obtained in step (1) is used as an electrolytic cell of a three-electrode system, with nickel foam as a working electrode, a platinum sheet as a counter electrode, and a calomel electrode as a reference electrode, and polymerized at a potential of 0.85 V for 800 seconds, and then washed and dried to obtain polymer nanofibers;

[0062] (3) immersing the polymer nanofibers obtained in step (2) in a 5 g / mL boric acid ethanol solution for 1 hour to obtain boron-doped nanofibers;

[0063] (4) The boron-doped nanofibers obtained in step (3) were placed in a tubular furnace and calcined at 900° C. for 30 minutes in an argon atmosphere to obtain boron-nitrogen-doped nanofibers, which were designated as BN-CNF / NF.

[0064] (5) Dissolve 0.05 mol nickel sulfate and 0.01 mol ferrous sulfate in 100 mL of deionized water to prepare an electrolyte;

[0065] (6) The solution obtained in step (5) was used as an electrolyte, the BN-CNF / NF obtained in step (4) was used as a working electrode, a platinum sheet was used as a counter electrode, and a Hg / HgO electrode was used as a reference electrode. Electrodeposition was performed at a potential of -5 V for 120 seconds. After washing and drying the electrodes, a boron-nitrogen-doped carbon nanofiber-based water electrolysis catalytic material was obtained, which was recorded as (BN-CNF@NiFe) / NF.

[0066] Comparative Example 1

[0067] The method for preparing a NiFe / NF catalyst comprises the following steps:

[0068] (1) Dissolve 0.09 mol nickel sulfate and 0.01 mol ferrous sulfate in 100 mL of deionized water to prepare an electrolyte;

[0069] (2) The solution obtained in step (1) was used as an electrolyte, nickel foam was used as a working electrode, a platinum sheet was used as a counter electrode, and a Hg / HgO electrode was used as a reference electrode. Electrodeposition was carried out at a potential of -5 V for 120 seconds. The electrodes were washed and dried to obtain a catalyst, which was recorded as NiFe / NF.

[0070] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention specification under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing an electrochemically prepared water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers, characterized in that: Here are the steps: a. Lithium perchlorate, pyrrole, sodium carbonate / sodium bicarbonate buffer, and deionized water were mixed and stirred to form a uniform mixture. Then, nickel foam was used as the working electrode and polymerization was carried out at a constant potential of 0.85 V under a three-electrode system for 800 seconds. The polymer was then impregnated with a boric acid solution to obtain an electrode on which boron-doped polymer nanofibers were grown. b The electrode obtained in step a was placed in an inert gas atmosphere in a tube furnace and calcined to obtain a boron and nitrogen-doped carbon nanofiber electrode; c. Mix nickel sulfate, ferrous sulfate and deionized water, stir and mix to form a uniform mixed solution, and then use a boron-nitrogen-doped carbon nanofiber electrode as a working electrode to perform electrodeposition at a constant potential of -5V for 120 seconds in a three-electrode system to obtain a water electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers; the water electrolysis catalytic material is a fiber core-shell structure catalyst composed of nickel-iron compounds wrapped around boron-nitrogen-doped carbon nanofibers.

2. The preparation method according to claim 1, characterized in that The molar ratio of pyrrole to lithium perchlorate is 0.1-10, the molar ratio of pyrrole to sodium carbonate is 0.1-10, the molar ratio of pyrrole to sodium bicarbonate is 0.1-10, and the molar ratio of H2O to pyrrole is 100-2000.

3. The preparation method according to claim 1, characterized in that The molar ratio of the nickel sulfate to other raw materials is: n(Ni) / n(Fe)=5-10, n(H2O) / n(Ni)=100-2000.

4. The preparation method according to claim 1, characterized in that The boric acid solution is one of boric acid aqueous solution, boric acid methanol solution, and boric acid ethanol solution, or a mixture of two or more thereof. The concentration of the boric acid solution is 1 g / mL to a saturated solution.

5. The preparation method according to claim 1, characterized in that The immersion time of the boric acid solution is 1 to 48 hours.

6. The preparation method according to claim 1, characterized in that The inert gas is one of helium, argon, and nitrogen, or a mixture of two or more.

7. The preparation method according to claim 1, characterized in that The calcination temperature is 400° C. to 1000° C., and the calcination time is 30 min to 200 min.

8. The electrolysis catalytic material based on boron-nitrogen-doped carbon nanofibers obtained by the preparation method according to any one of claims 1 to 7 is used as an electrode in the electrolysis of water in an alkaline solution.

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